Haptic actuators for producing vibration effects, i.e., vibration actuators such as eccentric rotating masses, linear resonant actuators, piezo based actuators, etc., are conventionally used in haptically enabled devices to provide vibration effects of moderate to long durations. Such haptic effects present to a user as buzzing or vibrating sensations. Providing a buzzing sensation can be implemented through excitation of a vibration actuator for many, e.g., dozens, hundreds, or even thousands of oscillations. Such vibration effects are implemented through conventional open loop control techniques of the vibration actuators. Precise actuator control over limited durations in these circumstances is not required and would introduce unnecessary costs in device manufacture.
In some circumstances, it may be desirable to produce haptic effects of limited duration, wherein a vibration actuator undergoes only a few, e.g., less than ten, oscillations. Such haptic effects may present to a user as clicks rather than buzzes. These types of clicks may be desirable, for example, to provide the sensation and satisfaction of a mechanical response to a touchscreen input. Conventionally, open loop control techniques and hardware are adapted to provide these short duration clicks by, for example, implementing actuator braking. To retain a high-quality well-defined sensation with a sharp edge through open loop braking may require good actuator characterization. Deviation in the actuator from the characteristics of the open loop control scheme can result in an effect that trails off rather than ends sharply. Thus, for example, variance from a specified resonant frequency of a linear resonant actuator can result in degraded limited duration haptic effects. Conventional solutions to this problem include post manufacture characterization of actuator outputs and adjustment of open loop control parameters.
Inventions described herein provided improved methods of generating limited duration haptic effects in haptically enabled devices.